The present invention relates to improving electrodes intended for electrolytic cells of the membrane type with vertical electrodes.
More particularly the invention relates to an electrode for an electrolytic cell of the membrane type, wherein one electrode is disposed vertically, is connected to an electric current lead along a horizontal zone, for example along its lower or upper edge zone, and is the seat of gas liberation. This electrode may be for example an anode or a cathode of a diaphragm cell for the electrolysis of water or of an aqueous solution of alkali metal halide or hydrochloric acid. A major difficulty met with in the design and use of electrolytic cells of the membrane type, with vertical electrodes, lies in the need to ensure regular evacuation of the gases (for example chlorine, oxygen or hydrogen) produced at the electrodes, in the body of the electrolyte. The presence of gas in the electrolyte, between the electrodes, in effect lowers noticeably the electrical conductivity of the electrolyte and, in consequence, lowers the energy yield of electrolysis.
Moreover, the upward motion of the gas in the electrolyte causes turbulence in the flow of electrolyte through the cell. A turbulent electrolyte flow has the disadvantage of subjecting the membrane to severe mechanical stresses. In order to avoid accelerated deterioration of the membrane, it is generally necessary to limit the height of the electrodes, to provide a wide spacing between the anodes and the cathodes of the cell and to limit the electrical current density, which is unfavourable both to the energy yield of the electrolytic cell and its productivity.
In order to diminish the aforesaid disadvantage of membrane cells with vertical electrodes, it has been proposed in French Pat. No. 2070757 of Nippon Soda Company Ltd., of Dec. 4, 1970, to utilize hollow anodes formed of metal plates, pierced by apertures and provided with horizontal gas deflectors sloping downwards, above the apertures, so as to direct the gas behind the plates.
These known foraminate anodes have, however, the disadvantage of possessing a very high electrical resistance. It is for this reason that, although they permit a noticeable reduction of the loss by Joule effect through the electrolyte in membrane cells, this advantage is largely offset by the disadvantage inherent in the excessive electrical resistance of these known foraminate anodes. Moreover, this very high electrical resistance necessitates a reduction in the height of the anodes so as to avoid an excessive potential gradient.
It has furthermore been found, in practice, that in membrane cells equipped with known foraminate anodes of this type the membranes tend to suffer accelerated and non-uniform deterioration, which can lead to local puncturing of the membranes.